An electronic control apparatus generally used for an engine control unit, an automatic transmission control unit and the like, mounted in a vehicle, has a structure in which a circuit board on which various electronic components are mounted is accommodated in a protective space (a waterproof space) inside an enclosure that is formed by connecting a plurality of enclosure members together. On this circuit board, besides the electronic component such as a capacitor, a heat-generating electronic component (hereinafter, a heat-generating component) such as a central processing unit (CPU) and a semiconductor switching element, which generates heat by its operation, is mounted.
As a method of radiating heat in the enclosure, which is generated by such heat-generating component, to the outside, a structure or configuration in which the heat generated by the heat-generating component is conducted to an inner wall surface of the enclosure member and the heat is radiated from an outer wall surface of the enclosure member into the air is adopted, then a method of suppressing high-temperature of the heat-generating component using this structure is employed. As this structure or configuration, there has been known a method in which a protruding portion that is a protuberance (or protrusion) protruding from a position on an inner wall surface side of the enclosure member, which faces the heat-generating component, toward the heat-generating component and located close to the heat-generating component (through a clearance) is formed, or a heat radiation member such as heat radiating material is interposed between the protruding portion and the heat-generating component (for instance, Patent Document 1).